It should provide you a lot of enjoyment.This is only my somewhat uneducated opinion.I think the Goldbeg cub has a much stronger wing structure,deciced after 2 rebuilds on my GP cub,presently it has a Goldberg wing,all that was left undamaged in a crash.I have crashed my Goldberg hard destroying the fuselage but no damage to wing,I beleive it has a pine dowel on leadsing edge and maybe heavier planking,might look into this differences when building see if you could beef up the GP.
I would buy the floats such as Goldbergs or GP if they have them leave the scratch building them to the more experienced flyers.Remember to beef up the bottom of the fuselage for the rear float mounts I use the front landing gear mount so no problem there.
Recently in another post about 4 cycles sounded like there power might be nice on a float plane,I was concerned about getting water into them but they seemed to think not a major issue,2-strokes I just dump out thew water and spin them till they start.Will try the 4cycle myself next spring.
THe Cub is a real nice float plane but as you can tell my bias is towrd the Goldberg but there is very little difference think it should serve you very well.GOOD LUCK.